The present invention relates to rappers for precipitators and, in particular, to reciprocatable hammers which may be mechanically driven to strike a target in the precipitator.
Electrostatic precipitators operate with an intense electrostatic field which ionizes exhaust gas to cause precipitation of particulate contaminants onto electrode plates in the precipitator. Since these contaminants adhere to the plates, they must be periodically cleaned to prevent clogging of the precipitator. A known technique for cleaning the plates is to strike a member supporting the precipitator plates so they vibrate and dislodge the precipitate thereupon. An inherent problem with such mechanisms is that any mechanical structure, especially gears and bearings, contained within the precipitator tends to become clogged itself with the precipitate. Another important design consideration for rappers is making their frequency and the magnitude of their impact variable. Such variation can be tailored to suit an unusually clean or dirty exhaust.
It is known to employ in a precipitator a rotating shaft carrying at least one hammer pivotally mounted off from the center of rotation of the shaft. The hammer, which can rotate only fractionally, is mounted within the precipitator adjacent to an anvil. Rotation of the shaft raises and inverts the hammer, after which it freely swings downwardly to strike the anvil.
Another known rapper has a reciprocatable lifter rotatably mounted at a different axis of rotation than a drive lever. The drive lever can employ a catch which engages and drives the lifter a predetermined amount before releasing it. A disadvantage with this type of apparatus is the large number of relatively moving parts and the high tolerances acquired to cause accurate operation and release of the rapper mechanism.
There are many known ways of mounting a rapper within a precipitator. Examples of the various rappers and other apparatus for dislodging dust, as well as their methods of mounting, are illustrated in U.S. Pat. Nos. 1,433,266; 1,551,724; 1,773,876; 2,547,573; and 4,221,573. In U.S. Pat. No. 1,433,266 a cam can reciprocate a frame to periodically lower it and knock it against a stationary member, thereby vibrating the precipitator structure and cleaning its plates. U.S. Pat. Nos. 1,551,724; 1,773,876 and 2,547,573 show various cams and mechanical structures used to clean a precipitator structure. U.S. Pat. No. 4,221,573 shows a pulley-type arrangement where an arcuate member rotates through a given angle before being released to drop a suspended weight against a structural member in a precipitator. Other known apparatus use electromechanical or air operated vibrators to accomplish the dislodging of dust adhering within a precipitator or dust collecting apparatus (eg. U.S. Pat. Nos. 333,021; 1,168,543; 2,550,809; and 2,702,090). U.S. Pat. Nos. 3,219,130 and 3,570,217 show the rotating of articulating hammers. These hammers, when rotated beyond a certain point, fall and swing faster than its driving shaft before impacting an anvil to create the vibration required to dislodge adhering dust.
Accordingly, there is a need for a simple and reliable rapper mechanism which can work in the dirty environment of a precipitator and yet be adjustable in frequency and impact magnitude.